Photo-multiplier circuit



May 29, 1951 F. WOUTERS PHOTO-MULTIPLIER CIRCUIT INVENTOR. Lou/5 E WOUTERS Filed Aug. 8, 1950 TW: @Qui NNY@ o m im C T ww mm 1w .lm

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,WLIVILILLKLIQLIWNLV QLI/ A T TOR/VEK Patented May 29, 1951 Louis F. Wouters, Oakland, Calif., assigner to the United States of America as represented by the United States Atomic Energy Commission Application August 8, 1950, Serial N0. 178,295

g s claims. wieso-sas) '.This invention relates to an electronic circuit and more particularly to a photo-multiplier circuit useful as a scintillation counter.

scintillation counters have been found useful in nuclear research since the earlier phases of such work. Experiments with iluorescent materials have been continuing and with the discovery of such materials having high intensity light pulses with very short resolving times-it has become necessary to improve the resolving time of the counting circuits. For example, with a material such as trans-stilbene a high intensity light pulse having a resolving time in the order of x10*9 second is produced. by bombardment of the material with charged particles. Comparing this resolving time with that of a conventional photo-multiplier and amplier arrangement, which is in the proximity of .25)(- second, the need of anew and improved circuit is readily apparent.

In order to obtain a circuit foruse with fluorescent materials having short resolving times the present invention utilizes a pair of photo-multiplier tubes with electrodes thereof interconnected in such a manner that the output of one controls the output of the other when the inputs to both are from a common source. 'Ihe output of the second tube is then available to trigger a gate circuit which in turn may be connected to a recording device or an oscilloscope. It will be readily apparent that many of the disadvantages of a single photo-multiplier circuit, such as random output pulses due to thermionic emission in the tubes and release of electrons at the cathode of one tube by bombardment, are eliminated.

It is therefore an object of the present invention to provide a new and improved photo-multiplier tube arrangement.

Another object of the present invention is to provide a pair of photo-multiplier tubes positioned to receive light from a single source and having electrodes thereof interconnected so that the output of one tube controls the output of the other tube.

Still another object of the present invention is to provide a pair of photo-multiplier tubes having electrodes interconnected to trigger a gate tube only when both photo-multiplier tubes are exposed to a commonsource of light.`

A further object of the present invention is to provide a photo-multiplier tube'circuit having an improved resolution time for handling pulses of very short duration. Y

A still further object of the present invention is to provide a photo-multiplier tube 'circuit free of spurious responses to emission occurring in one tube only.

Further objects and advantages will be apparent from the following description and claims 'considered together with the accompanying drawing which illustrates a schematic wiring diagram of the invention.

Referring to thedrawing in detail there is shown a light source I0 which may be a uorescent material, such as trans-stilbene, which iiuoresces upon excitation by bombarding charged particles, represented by an arrow II. Positioned to receive light from the source I8 are a vpair of similar nine-stage photo-multiplier tubes I5 and I6, each of which has a cathode I1, an anode I8 and nine intermediate electrodes, or dynodes-2i, 22, 23, 24, 25, 26, 21, 28, and 29 (consecutively numbered on the drawing from the cathode II to the anode I8). From the following it will be appreciated that photo-multiplier tubes having more or less than nine stages may be readily used. To supply operating potentials to the tube I5 a source of unidirectional voltage 3| is connected between the cathode II and the dynode 2l, a similar source 3I is connected between each of the dynodes 2l, 22, 23, 24, 25, 26, 21,-and 28 of the next seven stages, and a similar source 3| is connected between the last dynode 29 and the anode I8. In the form of the invention shown in the drawing the sources 3| have been illustrated as a series of batteries which will amply serve the purposes of the invention; however, it will be readily apparent that a single source of unidirectional voltage connected yacross a series of resistors which suitably divide the voltage 'may be used. Somewhat similarly, the operating potentials for the tube I6 are supplied to the elements thereof; that is, a voltage source 3| is connected between the cathode II and the dynode 2l, between each of the dynodes 2l, 22, 23, 24, 25, 26, and 2'I of the next six stages, between the dynodes 28 and 29 and between the dynode 29 and the anode I8. Interconnections between the two tubes I5 and I6 are provided by connecting the dynode 28 of the, tube I5 to the dynode 26 of the tube I6 and the dynode 29 of the former tube to the dynode 28 of the latter tube. A further connection of the tube I6 is made by connecting one end of a resister 36 to the dynode 2'I and the other end to the dynode 28. The action of the resistor 36 in the circuit will be more fully set forth hereinafter.

To utilize the circuit just described a connection 4| is made at the dynode 29 of the tube I6 and this connection 4I may be connected to the input terminal of an external circuit, such as a conventional gate circuit 46 illustrated in block form on the drawing. The output of the gate circuit is then available for connection to a recording device or an oscilloscope (not shown).

Now consider the operation of the invention arranged and connected in the above-described manner. The stream of charged particles II directed to strike the fluorescent material I causes scintillation. Because of the position of the photo-multiplier tubes I and IIB with respect to the fluorescent material I0, the light of the scintillations falls upon both of the cathodes I1 of the tubes resulting in photo-emission therefrom. The theory of operation of a photo-multiplier tube may be found in any textbook covering `the art of phototubes, for example, pages 514-516 of Theory and Applications of Electron Tubes by Reich, first edition, 1939. The potential of the sources 3| applied to the dynodes 2| to 28 of the tube I5 causes the emission to progressively travel from the cathode I1 to the successive dynodes, the emission increasing at each stage. A potential exists between dynodes 28 and 29 by reason of the source 3l and resistor 36 connected serially therebetween. Thus the emission continues its travel from dynode 28 to 29 and finally to the anode I3 of the tube I5. Similarly the emission from the cathode I1 of the tube ILG is amplified progressively to the dynode 21. It will be noted that there is no source 3| of potential connected between the dynodes 21 and 28, but that the resistor 36 is connected therebetween. In order for electrons to travel from dynode 21 to dynode 28 it is necessary that a voltage of sufficient magnitude exist between them and this voltage is dependent, in this instance, upon the current flow through the resistor 3S. Considering again the action taking place in tube I5, it is seen that when the electron emission reaches dynode 29 `of the tube, a current drain occurs from the respective potential source 3l through the resistor 36 thereby establishing a potential thereacros's. Since dynode 29 of the tube I5 is the last stage thereof, the emission has reached its maximum amplification and the potential across the resistor 35 biases the dynode 28 of the tube I6 to attract the emission of this latter tube from dynode 21. The emission from dynode 28 of the tube IS is then attracted to the dynode 29. By connecting the dynode 29 to the input of a gate circuit i6 the gate circuit is triggered and an output voltage occurs. As stated previously the output voltage of the gate circuit 46 maybe connected to a recording device or an oscilloscope as desired.

From the foregoing it is readily yapparent that it is necessary for photo-emission to occur simultaneously at the cathodes I1 of both tubes thereby eliminating any spurious emission which occurs in one tube only. It can also be seen that, by using one photo-multiplier tube to render a second photo-multiplier tube operative, a Well dened pulse of voltage at the output of the second tube is obtained, both as to pulse rise and' pulse cut off, thereby improving the resolution.

While the salient features of the invention have been described in detail with respect to one embodiment it will, of course, be apparent that numerous modifications may be made within ther spirit and scope of the invention and it is therefore not desired to limit this invention to the exact details shown except insofar as they may be defined in the following claims. Y

What is claimed is:

1. In a photo-multiplier tube circuit, the combination comprising a source of light pulses, a iirst and a second photo-multiplier tube disposed adjacent said source of light to receive light pulses therefrom, each of said tubes having a cathode, an anode, and a plurality of intermediate dynoiies, means vconnected between a pair of dynodes of said first tube for developing a voltage proportional to the current flow between said pair of dynodes, a portion of said means being connected between a pair of dynodes 'of said .second tube, and voltage supply means connected to the other electrodes of said iirst and second tubes to furnish operating voltages thereto, whereby the amplified emission in said rst tube is utilized lto bias a dynode of said second tube to further amplify the emission in said second tube.

2. In a photo-multiplier tube circuit, the combination comprising a source of light pulses, a first and a second photo-multiplier tube disposed adjacent said source of light to receive light pulses therefrom, each of said tubes having a cathode, an anode, and a plurality of intermediate dynodes, means connected between the iinal two dynodes of said rst tube for developing a voltage proportional to the current fiow between said iinal two dynodes, a portion of said means being connected between an adjacent pair of dynodes of said second tube which precede the iinal dynode thereof, and voltage supply means connected to the other electrodesA of said first and secondtubes to furnish operating voltages thereto, whereby the amplified emission in said rst tube is utilized to bias a dynode of said second tube to further amplify the emission in said second tube.

3. In a photo-multiplier tube circuit, the combination comprising a source of light pulses, a first and a lsecond photo-multiplier `tube disposed adjacent said source of light to receive light pulses therefrom, each-of said tubes having a cathode,- an anode, and a plurality of intermediate dynodes, a series circuit including a source of voltage and a resistor connected between the final twodynodes of said first tube, said source of voltage being connected between two adjacent dynodes of said second tube, said resistor being connected to a third dynode of said `second tube which is adjacent to the pair connected to the voltage source, voltage supply means connected to the other electrodes of saidfirst and second tubes to furnish operating voltages thereto, and an output lead' connected to the final dynode of said second tube for connection to an external circuit.

4. In a photo-multiplier tube circuit, the combination comprising a source of light pulses, a

first and a second- .photo-multiplier tube disposed' adjacent said source of light to receive light pulses therefrom, each of said tubes having a cathode, an anode, and a plurality of intermediate dynodes, a series circuit having a first portion and a second portion connected between the nal two dynodes of said first tube, said first portion supplying a iicw of current through said second portion when emission occurs in said rst tube, said first portion also being connected between a pair of adjacent dynodes of said second tube, saidsecond portion being connected to a'third dynode adjacent said pair of dynodes in said second tube, wherebythe voltage across said second .portion .due to current iiow therethrough impressed, and voltage supply means connected to the other electrodes to furnish operating voltages thereto, whereby the amplied emission in said rst tube is utilized to bias a dynode of said second tube to Afurther amplify the emission in said second tube.

5. In a photo-multiplier tube circuit, the combination comprising a source of light pulses, a rst and a second photo-multiplier tube disposed adjacent said source of light t0 receive light pulses therefrom, each of said tubes having a. cathode, an anode, and a plurality of intermediate dynodes, a series circuit including a source of voltage and a resistor connected be tween the nal two dynodes of said rst tube, said source of voltage being. connected between two adjacent dynodes of said second tube, said resistor being connected to a third dynode of said second tube which is adjacent to the pair LOUIS F. WOUTERS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,304,755 Zworykin Dec. 8, 1942 2,517,404 Morton Aug. 1, 1950 

